The invention concerns a device for applying pressure to the surface of such an advancing workpiece as plywood for example, against which at least one continuous belt is forced by fluid introduced into an inflatable pad demarcated by part of one of the pressure-application belt's strands, on the side facing the strand by a rectangular slab, and at the longitudinal and transverse edges of the slab in terms of the direction the belt travels in by a sealing strip of plastic or similar material at the edge of the slab and resting against the belt.
A device of this type is known (from German Patent 3 313 406). The strip is fastened to a rectangular frame. The frame is secured in a groove in the slab, moves in and out of the groove and is forced toward the belt. The belt travels along the strip.
The strips and belts in two-belt presses that employ fluid-inflated pads seal the pad off from the atmosphere. The belts are steel.
Such presses operate continuously, and the strips must satisfy high demands to ensure that the pad is reliably sealed no matter what state the press is in. The belt travels at a wide range of speeds, and the friction between it and the strip must be low no matter how rapidly it is traveling. The strip must also be resistant to heat over a wide range of temperatures. Finally, the strip must be long-lasting.
Such strips are made out of slippery and heat-resistant plastics.
In order to comply even more satisfactorily with the aforesaid demands, distributing nozzles or channels along the strip to deliver lubricant directly to the seal interface is known (European Patent B 0 166 886).
Sealing strips thus lubricated operate satisfactorily up to moderate pressures. At higher pressures, however, the film of lubricant is forced out of the interface too rapidly. Another drawback is the rather high price per kilogram of the special-purpose oils required.
Also known are self-lubricating low-friction components in the form of sleeves and plates made of solid lubricants in a metal matrix. Such components, however, are inappropriate for sealing off pads in belt presses. Subject to the high pressure and heat that occurs, metal particles are hurled out, especially at low belt speeds, and lead to fretting and freezing and hence to damage to the sensitive surface of the steel belt.